MMT/AO 5 micron Imaging Constraints on the Existence of Giant Planets Orbiting Fomalhaut at ~13-40 AU

A candidate < 3 Jupiter mass, extrasolar planet was recently imaged by Kalas et al. (2008) using HST/ACS at 12.7" (96 AU) separation from the nearby (d = 7.7 pc) young (~200 Myr) A2V star Fomalhaut. Here we report results from M-band (4.8 micron) imaging of Fomalhaut on 5 Dec 2006 using the Clio IR imager on the 6.5-m MMT with the adaptive secondary mirror. Our images are sensitive to giant planets at orbital radii comparable to the outer solar system (~5-40 AU). Comparing our 5-sigma M-band photometric limits to theoretical evolutionary tracks for substellar objects, our results rule out the existence of planets with masses greater than 2 Jupiter masses, from ~13-40 AU and objects greater than 13 Jupiter masses from ~8-40 AU.